If several debtors owe a performance in such a way that each of them is obliged to effect the entire performance, but the creditor is only entitled to demand the performance once, the creditor may demand the performance from each of the debtors in whole or in another part at his discretion. Until the entire performance has been effected, all debtors remain obligated (§ 421 BGB).
If two persons are jointly and severally liable, the creditor can claim the entire debt from one of them. However, one person can then recover his or her share from the other person (the other debtor) in a so-called internal settlement.